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The DOP Network Object contains a DOP simulation. Simulations can consist of any number of simulation objects (which do not correspond to Objects that appear in /obj). These simulation objects are built and controlled by the DOP nodes contained in this node.

Simulation-wide controls are provided on this node, such as caching options and time step controls. The entire simulation can also be transformed using the Transform parameters of this node. Transforming a simulation at this level does not affect the simulation at all. The Transform is applied after the simulation occurs.

Tip

To improve the playback of cached fluids, increase the **Cache Memory** on the **Simulation** tab.

## Parameters

Playback Simulation

Turns the DOP network into a player for simulation files. Enabling playback mode will cause the result of the DOP network to be given by the simulation files selected. The internal nodes of the network will be ignored. One way to create simulation files to play using this option is the Output Node inside the DOP network.

## Simulation

Reset Simulation

Полностью очищает кэш симуляции. В момент просмотра сети DOP над вьюпортом с правой стороны будет активирована кнопка. Нажатие этой кнопки выполняет те же действия, что и нажатие кнопки Reset Simulation.

Display

Whether the simulation is displayed in the viewport.

Initial State

The name of a file that is used as the initial state of the simulation. This file must be a simulation state file created by either a File DOP or a Dynamics Output Driver. If this parameter is set, then the DOP nodes inside this network are not processed on the first simulation timestep.

Timestep

Controls the length of a simulation timestep. Usually this value will be some multiple of a frame time, but it is not required. By specifying a larger timestep the simulation will run faster but will be less accurate and less stable. Smaller timesteps give better result but calculate more slowly.

Substeps

The default timestep expression will use this parameter to control how many substeps the dop simulation should perform every frame. This can be easier to adjust than working with the 1/$FPS parameter in timestep.

Offset Time

Specifies an offset in seconds between the simulation time
for this simulation and the global time displayed on the
playbar. If this parameter is set to 1, then this simulation
will not start cooking until frame 25. At that global time
of 1 second, the simulation time will be 0. Several
expression functions such as `doptime`

exist for converting
from global times to simulation times and vice versa.

Start Frame

Выражение по смещению времени ссылается на этот параметр. Это позволяет установить время начала симуляции в кадрах, а не в секундах, что в некоторых случаях может быть более удобным. Если для начального кадра установлено значение 24, симуляция не начнется до 24 кадра. Обратите внимание, что если вы используете этот параметр, то переменные $SF и $F больше не будут ссылаться на то же время внутри симуляции.

Scale Time

Указывает множитель, который соотносит глобальное время с временем внутри симуляции для данной сети DOP. Значение больше единицы означает, что время симуляции протекает быстрее, чем глобальное время. Значение меньше единицы приводит к тому, что симуляция происходит в замедленном движении относительно глобального времени. Существуют несколько выражений функций, таких как `doptime`

, для преобразования глобального времени в время внутри симуляции и обратно.

Max Feedback Loops

When simulation objects using different solvers are made to be mutual affectors (such as a cloth object and an RBD object), this parameter controls the maximum number of iterations to perform while attempting to resolve the two solvers. Increasing this number in situations where different solvers are mutual affectors increases the ability of the simulation to reach a satisfactory result, but can increase the simulation calculation time.

In the case of fluid simulations, since the fluid cannot adapt to the feedback forces that are applied, a value of 2 should be used rather than higher values. Higher values will just make the fluid artificially stronger and take considerable time.

Enable Automatic Resimulation

When any parameter inside a DOP simulation is changed, or when any referenced external node is changed, the cache of the simulation is marked as invalid. If this parameter is turned on, the next time the playbar is moved to reach a simulation time of 0, the cache will be cleared and the first simulation timestep will be recalculated. If the cache is invalidated while at a simulation time of 0, the initial state is recalculated immediately. If the current time is beyond time 0, then the most recent timestep will be recooked, and the cache beyond the current time will be cleared. But all prior timesteps will be left untouched other than to be marked invalid. If this parameter is off, the cache is marked as invalid in exactly the same way, but the cache is never cleared automatically. To recook a simulation in this mode, the Recook Simulation button on this parameter dialog or above the viewport must be used.

Provide Data Hints

Rules governing allowed simulation data relationships are stored in a files called dophints.cmd in the scripts directory. If this option is turned on, at the end of each timestep the simulation state is compared against the rules in that file. If any rules are broken, warnings are added to the appropriate DOP nodes. This can be very useful when learning to use DOPs or when debugging problems with a simulation. Turning this option off will improve the performance of your simulation by skipping this validation step at the end of each timestep.

Interpolate Display Data

If the global time is set to a value that does not line up with a simulation timestep boundary, this parameter controls how the simulation should be displayed. If this parameter is turned off, the closest simulation timestep contents are displayed. If this parameter is turned on, the contents of the previous and next simulation timesteps are interpolated to create an approximation of the simulation as it would have actually been at the current time. This option allows the simulation to appear smooth in the viewport even if the simulation timesteps do not line up with the global frame times.

## Cache

Cache Simulation

Активирует кэш симуляции. Если эта опция не включена, многие солверы не будут работать должным образом. Однако для очень больших симуляций выключение этой опции - лучший способ гарантировать наименьший возможный объем памяти для симуляции.

Compress .sim Files

Determines if .sim files written to disk for caching will be compressed. Compression can reduce the size of the disk cache significantly, but can also increase the time to cache significantly. If loading or writing to cache seems slow, try using blosc compressed .sim files or uncompressed .sim files, especially with fluid sims.

Allow Caching To Disk

If the maximum size of the cache in memory is reached, the DOP Network can either delete old cache entries to make room for new entries, or old entries can be saved to disk. If this option is on, the old cache entries are saved to disk and will be reloaded from disk if needed. This mode will be slower than simply throwing away the old cache entries, but it ensures that the entire simulation history is always available regardless of the in-memory cache size.

Cache to Disk in Non Interactive Sessions

In non-interactive sessions, such as hscript or hython, one may often not want the entire simulation history to be available. Their default behavior is to ignore the Allow Caching to Disk and not cache to disk. This behavior can be overridden with this toggle. Saving old simulation states to disk can often become very expensive and, since one will not be scrubbing the playbar on the result, a waste of disk space.

Cache Substep Data

Some solvers perform their own internal subsampling of time to get better results. This option controls whether or not the substep data created during this internal subsampling should be kept as part of the cache, or discarded as soon as the simulation timestep has finished computing. Having this option on can be useful for debugging purposes, or if accurate display of sub-timestep data is desired. Using the actual substep data will give more accurate results that displaying interpolated data.

Cache Memory (MB)

Specifies how much memory in megabytes can be consumed by the cache for this simulation. Once this limit is exceeded, old cache entries are either deleted or saved to disk to make more room, depending on the value of the Allow Caching To Disk parameter value above.

Timeless (No History)

Each frame the simulation is started fresh as if it were the first frame. This means $SF is always 1. It also means, however, if the network consists of a File DOP with a $F based .sim file, only the current frame will have to be loaded, allowing for fast random access of baked simulations. Note that when in this mode only one frame is kept in the cache.

Save Checkpoints

Normally when the Allow Caching to Disk is enabled and the simulation hits the memory limit, the simulation is saved to files in the temp directory. While these are valid .sim files, they can be hard to manage. When this options is on, each frame is immediately cached to the specified directory. It is still kept in memory until the Cache Memory is hit, but at that point it is not saved to disk (since it’s already on disk). The advantage of checkpointing is that if a cache frame already exists DOPs will not cook that frame, even if the simulation has been reset. Instead it will load that frame. Further, it only needs to cook the frames after the last valid checkpoint frame before the requested frame. So if you have cache_50.sim and try to cook frame 100, cooking can start at frame 50.

Using save checkpoints is similar to using a File DOP in Automatic Mode. However, when you try to jump to frame 50 with a File DOP it must load the first 50 frames. With checkpoints it can skip this step.

Checkpoint Files

The file sequence to save the checkpoints to. These are .sim files, loadable with the File DOP or File SOP. The variable $SF must be used to specify the frame number - $F cannot be used because this is working in simulation space. $SF4 is also supported.

Checkpoint Trail Length

How much of a history to keep before the checkpoint files are deleted. A value of 0 will never delete cache files. Otherwise, frames older than this value will be erased from disk.

Note that only checkpoint files created by this session of Houdini will be deleted. If you restart Houdini with an existent cache files, they will not be deleted. This is done because you were likely restarting from a crashed location and will want to guarantee you can once again restart there if it crashes again.

Checkpoint Interval

The frame interval between checkpoints. Setting this to a value of 1 will save a checkpoint every frame. Setting this to higher values will save a checkpoint after every number of frames specified. For example setting this to 5 will save a checkpoint every 5 frames.

This can be done to save disk space if you are running a large simulation.

### Transform

Transform Order

The left menu chooses the order in which transforms are applied (for example, scale, then rotate, then translate). This can change the position and orientation of the object, in the same way that going a block and turning east takes you to a different place than turning east and then going a block.

The right menu chooses the order in which to rotate around the X, Y, and Z axes. Certain orders can make character joint transforms easier to use, depending on the character.

Translate

Translation along XYZ axes.

Rotate

Degrees rotation about XYZ axes.

Scale

Non-uniform scaling about XYZ axes.

Pivot

Local origin of the object. See also setting the pivot point .

Uniform Scale

Scale the object uniformly along all three axes.

Modify Pre-Transform

This menu contains options for manipulating the pre-transform values. The pre-transform is an internal transform that is applied prior to the regular transform parameters. This allows you to change the frame of reference for the translate, rotate, scale parameter values below without changing the overall transform.

Clean Transform

This reverts the translate, rotate, scale parameters to their default values while maintaining the same overall transform.

Clean Translates

This sets the translate parameter to (0, 0, 0) while maintaining the same overall transform.

Clean Rotates

This sets the rotate parameter to (0, 0, 0) while maintaining the same overall transform.

Clean Scales

This sets the scale parameter to (1, 1, 1) while maintaining the same overall transform.

Extract Pre-transform

This removes the pre-transform by setting the translate, rotate, and scale parameters in order to maintain the same overall transform. Note that if there were shears in the pre-transform, it can not be completely removed.

Reset Pre-transform

This completely removes the pre-transform without changing any parameters. This will change the overall transform of the object if there are any non-default values in the translate, rotate, and scale parameters.

Keep Position When Parenting

When the object is re-parented, maintain its current world position by changing the object’s transform parameters.

Child Compensation

When the object is being transformed, maintain the current world transforms of its children by changing their transform parameters.

Enable Constraints

Enable **Constraints Network** on the object.

Constraints

Path to a CHOP **Constraints Network**.
See also creating constraints.

Tip

You can you use the Constraints drop down button to activate one of the Constraints Shelf Tool. If you do so, the first pick session is filled automatically by nodes selected in the parameter panel.

Note

Lookat and Follow Path parameters on object nodes are deprecated in favor of Look At and Follow Path constraints. The parameters are only hidden for now and you can set their visibitily if you do edit the node’s parameter interface.

## Examples

The following examples include this node.

CountImpacts Example for Count channel node

DynamicLights Example for Dynamics channel node

DynamicPops Example for Dynamics channel node

ExtractTransforms Example for Dynamics channel node

AnimatedActiveState Example for Active Value dynamics node

AutoFreezeRBD Example for Active Value dynamics node

SimpleAffector Example for Affector dynamics node

LookAt Example for Anchor: Align Axis dynamics node

ApplyRelationship Example for Apply Relationship dynamics node

BridgeCollapse Example for Apply Relationship dynamics node

ConstrainedTeapots Example for Apply Relationship dynamics node

MutualConstraints Example for Apply Relationship dynamics node

SimpleBlend Example for Blend Solver dynamics node

BuoyancyForce Example for Buoyancy Force dynamics node

AnimatedClothPatch Example for Cloth Object dynamics node

BendCloth Example for Cloth Object dynamics node

BendDamping Example for Cloth Object dynamics node

BlanketBall Example for Cloth Object dynamics node

ClothAttachedDynamic Example for Cloth Object dynamics node

ClothFriction Example for Cloth Object dynamics node

ClothUv Example for Cloth Object dynamics node

DragCloth Example for Cloth Object dynamics node

MultipleSphereClothCollisions Example for Cloth Object dynamics node

PanelledClothPrism Example for Cloth Object dynamics node

PanelledClothRuffles Example for Cloth Object dynamics node

AnchorPins Example for Constraint Network dynamics node

AngularMotorDenting Example for Constraint Network dynamics node

BreakingSprings Example for Constraint Network dynamics node

Chains Example for Constraint Network dynamics node

ControlledGlueBreaking Example for Constraint Network dynamics node

GlueConstraintNetwork Example for Constraint Network dynamics node

Hinges Example for Constraint Network dynamics node

PointAnchors Example for Constraint Network dynamics node

SpringToGlue Example for Constraint Network dynamics node

AutoFracturing Example for Copy Objects dynamics node

SimpleCopy Example for Copy Objects dynamics node

CrowdHeightField Example for Crowd Solver dynamics node

FollowTerrain Example for Crowd Solver dynamics node

FootLocking Example for Crowd Solver dynamics node

Formation Crowd Example Example for Crowd Solver dynamics node

Stadium Crowd Example Example for Crowd Solver dynamics node

Street Crowd Example Example for Crowd Solver dynamics node

ClipTransitionGraph Example for Crowd Transition dynamics node

TypesOfDrag Example for Drag Force dynamics node

FieldForceSmoke Example for Field Force dynamics node

FromRBD Example for Field Force dynamics node

SimpleField Example for Field Force dynamics node

fieldforce Example for Field Force dynamics node

CacheToDisk Example for File dynamics node

FEMSpheres Example for finiteelementsolver dynamics node

DensityViscosity Example for FLIP Solver dynamics node

FlipColorMix Example for FLIP Solver dynamics node

FlipColumn Example for FLIP Solver dynamics node

FlipFluidWire Example for FLIP Solver dynamics node

SpinningFlipCollision Example for FLIP Solver dynamics node

VariableViscosity Example for FLIP Solver dynamics node

FluidWireInteraction Example for Fluid Force dynamics node

BallInTank Example for Fluid Object dynamics node

FillGlass Example for Fluid Object dynamics node

FluidFeedback Example for Fluid Object dynamics node

PaintedGrog Example for Fluid Object dynamics node

RestartFluid Example for Fluid Object dynamics node

RiverBed Example for Fluid Object dynamics node

VariableDrag Example for Fluid Object dynamics node

HotBox Example for Gas Calculate dynamics node

DiffuseSmoke Example for Gas Diffuse dynamics node

CombinedSmoke Example for Gas Embed Fluid dynamics node

EqualizeFlip Example for Gas Equalize Volume dynamics node

EqualizeLiquid Example for Gas Equalize Volume dynamics node

dopexample_gasnetfetchdata Example for Gas Net Fetch Data dynamics node

TeapotUnderTension Example for Gas Surface Tension dynamics node

UpresRetime Example for Gas Up Res dynamics node

GuidedWrinkling Example for Hybrid Object dynamics node

MagnetMetaballs Example for Magnet Force dynamics node

SimpleMagnets Example for Magnet Force dynamics node

MaskedField Example for Mask Field dynamics node

SimpleMultiple Example for Multiple Solver dynamics node

VolumeSource Example for Particle Fluid Emitter dynamics node

FluidGlass Example for Particle Fluid Solver dynamics node

PopFlow Example for Particle Fluid Solver dynamics node

PressureExample Example for Particle Fluid Solver dynamics node

ViscoelasticExample Example for Particle Fluid Solver dynamics node

ViscousFlow Example for Particle Fluid Solver dynamics node

WorkflowExample Example for Particle Fluid Solver dynamics node

AdvectByFilaments Example for POP Advect by Filaments dynamics node

AdvectByVolume Example for POP Advect by Volumes dynamics node

ParticlesAttract Example for POP Attract dynamics node

ParticlesIntercept Example for POP Attract dynamics node

PointAttraction Example for POP Attract dynamics node

SphereAxisForce Example for POP Axis Force dynamics node

TorusAxisForce Example for POP Axis Force dynamics node

ParticleCollisions Example for POP Collision Detect dynamics node

CurveForce Example for POP Curve Force dynamics node

FlockInPops Example for POP Flock dynamics node

BaconDrop Example for POP Grains dynamics node

KeyframedGrains Example for POP Grains dynamics node

TargetSand Example for POP Grains dynamics node

VaryingGrainSize Example for POP Grains dynamics node

SwarmBall Example for POP Interact dynamics node

LookatTarget Example for POP Lookat dynamics node

DragCenter Example for POP Property dynamics node

ProximateParticles Example for POP Proximity dynamics node

CrossTheStreams Example for POP Stream dynamics node

BillowyTurbine Example for Pyro Solver dynamics node

DampedHinge Example for RBD Angular Spring Constraint dynamics node

SimpleRotationalConstraint Example for RBD Angular Spring Constraint dynamics node

Stack Example for RBD Auto Freeze dynamics node

RagdollExample Example for Cone Twist Constraint dynamics node

ShatterDebris Example for RBD Fractured Object dynamics node

StackedBricks Example for RBD Fractured Object dynamics node

Pendulum Example for RBD Hinge Constraint dynamics node

SimpleKeyActive Example for RBD Keyframe Active dynamics node

DeformingRBD Example for RBD Object dynamics node

FrictionBalls Example for RBD Object dynamics node

RBDInitialState Example for RBD Object dynamics node

SimpleRBD Example for RBD Object dynamics node

ActivateObjects Example for RBD Packed Object dynamics node

AnimatedObjects Example for RBD Packed Object dynamics node

DeleteObjects Example for RBD Packed Object dynamics node

EmittingObjects Example for RBD Packed Object dynamics node

SpeedLimit Example for RBD Packed Object dynamics node

Chain Example for RBD Pin Constraint dynamics node

Chainlinks Example for RBD Pin Constraint dynamics node

Pendulum Example for RBD Pin Constraint dynamics node

popswithrbdcollision Example for RBD Point Object dynamics node

GravitySlideExample Example for Slider Constraint dynamics node

DegreesOfFreedom Example for RBD Solver dynamics node

PaddleWheel Example for RBD Solver dynamics node

Weights Example for RBD Spring Constraint dynamics node

InheritVelocity Example for RBD State dynamics node

Simple Example for RBD Visualization dynamics node

ReferenceFrameForce Example for Reference Frame Force dynamics node

RippleGrid Example for Ripple Solver dynamics node

Freeze Example for Script Solver dynamics node

ScalePieces Example for Script Solver dynamics node

SumImpacts Example for Script Solver dynamics node

2dfluid Example for Smoke Object dynamics node

DelayedSmokeHandoff Example for Smoke Object dynamics node

Open CL smoke Example for Smoke Object dynamics node

RBDtoSmokeHandoff Example for Smoke Object dynamics node

SourceVorticlesAndCollision Example for Smoke Object dynamics node

rbdsmokesource Example for Smoke Object dynamics node

VolumePreservingSolid Example for Solid Object dynamics node

DentingWithPops Example for SOP Solver dynamics node

VisualizeImpacts Example for SOP Solver dynamics node

StaticBalls Example for Static Object dynamics node

FractureExamples Example for Voronoi Fracture Solver dynamics node

SimpleVortex Example for Vortex Force dynamics node

TurbulentSmoke Example for Wind Force dynamics node

AnimatedSkin Example for Wire Glue Constraint dynamics node

CompressedSpring Example for Wire Object dynamics node

BeadCurtain Example for Wire Solver dynamics node

BendingTree Example for Wire Solver dynamics node

BreakWire Example for Wire Solver dynamics node

CurveAdvection Example for Wire Solver dynamics node

Pendulum Example for Wire Solver dynamics node

PackedFragments Example for Assemble geometry node

FadedTorus Example for Attribute Fade geometry node

CaptureDeform Example for Cloth Deform geometry node

LowHigh Example for Dop Import geometry node

ProxyGeometry Example for Dop Import geometry node

dopimportrecordsexample Example for DOP Import Records geometry node

ColourAdvect Example for Fluid Source geometry node

CoolLava Example for Fluid Source geometry node

glueclusterexample Example for Glue Cluster geometry node

PartitionBall Example for Partition geometry node

AlphaOmega Example for Points from Volume geometry node

PlateBreak Example for TimeShift geometry node

TransformFracturedPieces Example for Transform Pieces geometry node

Fuzzy Logic Obstacle Avoidance Example Example for Fuzzy Defuzz VOP node

Fuzzy Logic State Transition Example Example for Fuzzy Defuzz VOP node

RampParameter Example for Parameter VOP node